Cryptid odds of existence
The possibility of birds or insects or other small mammals thought to be extinct or non existant existing today, odds wise, is pretty good in my opinion. The thought of Bigfoot or any other large creature existing today seems unlikely unless it's living in the Congo region.
Most oceanic cryptids i think are more likely than land ones. Anything dating back to the prehistoric times could easily still be lurking in the depths of the oceans. I'll list a few cryptids and put my percentage of possiblity of existing today after it. Feel free to add your own:
Bigfoot: 2%
Nessie or Champ: 1%
Thunderbird: 10%
Megaladon Shark: 20%
Mokele-mbembe: 30%